Optically Tunable Multistable Liquid Crystal Grating for Anti-Counterfeiting through Multilayer Continuous Phase Analysis

Optically tunable liquid-crystal (LC) gratings have remarkable applications in the field of image analysis for anti-counterfeiting. However, existing tunable LC gratings suffer from limited adjustable ranges and weak stability. The spacing variability and accuracy of the grating cannot satisfy the demands of continuous analysis. This study presents a novel approach to anti-counterfeiting through multilayer continuous phase analysis (MCPA) based on the continuous multistable states of the LC grating. This optically tunable LC grating featuring continuous multistable states is successfully prepared using a novel optically tunable chiral dopant, tetra(n-hex-azo), which exhibits an exceptionally slow conformational relaxation rate (half-life: 78.02 h). By exposing the LC grating to ultraviolet irradiation with an intensity of 0.1054 mW cm-2, the fringe spacing can be continuously and widely tuned between 0 and 250 mu m, which enhances the ultraslow conformational relaxation of tetra(n-hex-azo). Four representative spacings (50, 55, 60, and 65 mu m) are selected to construct four-layer MCPA gratings, enabling simultaneous decoding of a four-layer latent image for the first time. The mechanism of the MCPA grating is investigated through control experiments and theoretical simulations. This study demonstrates a facile, precise, and efficient approach for complex information encryption and anti-counterfeiting. An optic-tunable continuous liquid crystal (LC) grating is constructed with a unique photosensitive chiral dopant Tetra(n-hex-azo) featuring continuous multistable states, and it is utilized to develop multi-layer continuous phase analysis (MCPA) technology for anti-counterfeiting. image